Fibre composite plastic (FCP) laminates differ from monolithic metals in particular in that they have a layered structure. Sudden loading, for example, can therefore lead to two mutually bordering layers becoming detached from each other (also referred to as “delamination”). In order to avoid such failure behaviour, there are various approaches for reinforcing FCP laminates by means of fibres running perpendicularly to the layers (referred to hereinafter as the third spatial direction).
A first approach to be mentioned in this connection involves the sewing methods. A distinction must be drawn in this regard between two-sided and one-sided sewing methods:
Two-sided sewing methods are distinguished by an upper and a lower thread. The needle pierces, together with the upper thread, through the FCP laminate. On the underside of the FCP laminate, the loop of the upper thread is fixed by means of the lower thread. The needle is retracted and plunges in again at a defined distance from the preceding stitch. Through repetition, this produces a continuous seam.
One-sided sewing methods are distinguished in that they do not have a lower thread. These methods include for example tufting or blind-stitching.
Sewing methods have been found to have the drawback that the needles are comparatively thick, causing marked fibre displacements in the FCP laminates. The quantity of fibres that can be introduced by means of sewing methods is also low compared to the cavities which are formed in the FCP laminates by the insertion of the needle.
A second known approach for reinforcing FCP laminates in the third spatial direction utilises semi-finished products which are already provided with a matrix and cured, in particular pins. These pins are manufactured for example by pultrusion, inserted into the FCP laminates in the third spatial direction by piercing them and fixed by means of the matrix in the FCP laminates.
In the method according to the second approach, the introduction of the pins has proven to be very complex and thus cost-intensive.
The applicant therefore developed a better method for reinforcing semi-finished textile products in the third spatial direction that is described in DE 102005024408 A1 and will be briefly outlined hereinafter with reference to FIG. 1 to 4.
FIG. 1 shows a hook needle 8 prior to insertion into a semi-finished textile product 1. The semi-finished textile product is for example a fibre ply in which the fibres extend, as shown, in the x-y plane. As shown in FIG. 1, the needle 8 is at an angle α of <90 degrees to the third spatial direction z. The needle therefore has a component in the third spatial direction z.
FIG. 2 shows a stage of the manufacturing method at which the needle 8 has just pierced the semi-finished textile product 1 with its tip which has an eye 5. Located below the semi-finished textile product 1, in the region of the point at which the needle 8 emerges, is a roving 3 (for example a 24 K roving) which has been shaped, in close proximity to the underside of the semi-finished textile product 1, to form a loop. The roving 3 is picked up by the needle 8 by means of the eye 5. The roving 3 has a single thickness S, so that the roving from FIG. 2, which is folded to form the loop, has a roughly double thickness 2S.
In FIG. 3 the needle 8 is already being retracted again from the semi-finished textile product 1 and, as a consequence of this retraction, the roving 3, which is picked up by the needle 8, is drawn at the underside of the semi-finished textile product 1 into the through-hole 2 formed by the needle 8 during insertion, thus compressing the roving 3.
In FIG. 4 the entire roving 3 has been drawn into the semi-finished textile product 1, the needle 8 already having been uncoupled from the roving 3. The roving 3 can now for example be cut off flush on both sides of the semi-finished textile product 1 in order subsequently to infiltrate the through-hole 2 and the roving 3 arranged therein with a resin.
Roving material is usually provided as an endless roving which is wound for example onto a bobbin. In order now to obtain the cut-to-length roving 3 which is shown in FIG. 3 and has a length adapted to the thickness (in the z direction) of the semi-finished textile product 1, the cut-to-length roving must be separated off from the endless roving and must be provided to the eye 5 of the needle 8 below the semi-finished textile product 1.
Manually providing the roving 3 in FIG. 2 is impractical for reasons of cost. There is therefore need for a device which provides the roving 3 in an automated manner. No such device is at present commercially available.